We also took our Siamese cat cruising for 2 years from maine to South America and back. She was akitten when we left so she really knew no other life and di absolutely fine. Very happy cat.
I do NOT agree with the poster above who recommended declawing the cat. Then how would they climb back aboard (assuming you leave a fat knotted rope, towel, or other "ladder" for them) when the fall overboard?
Daisy once fell overboard in the middle of the night while at anchor in the BVI. Luckily I heard the splash and woke up. We'd tried to train her to use the rope "ladder" but who knows if she would have made it alone? She was swimming up to the bow (not the stern where the "ladder" was) when we got on deck. After that, she slept in the V-berth with our daughter with the door closed at night.
We did not have any trouble with officials anywhere in the Caribbean, South and Central America. We had vet papers but no one except the Bahamas asked to see them. Just check restrictions in advance; your choice of destinations might be limited in some cases.
We loved having Daisy on board with us. I'd highly recommend it, particluarly if you start a kitten off on board.
Kitty litter was the worst part. Hard to find some places, and messy. We kept one of those faux-grass doormats (which we'd originally purchased to try to use in lieu of kitty litter, as we'd heard some cruisers do) in front of the covered litter box. It trapped MOST of the stray litter as she walked across it on her way out.